New spectral imaging techniques for blood oximetry in the retina

Abstract

Hyperspectral imaging of the retina presents a unique opportunity for direct and quantitative mapping of retinal biochemistry -particularly of the vasculature where blood oximetry is enabled by the strong variation of absorption spectra with oxygenation. This is particularly pertinent both to research and to clinical investigation and diagnosis of retinal diseases such as diabetes, glaucoma and age-related macular degeneration. The optimal exploitation of hyperspectral imaging however, presents a set of challenging problems, including; the poorly characterised and controlled optical environment of structures within the retina to be imaged; the erratic motion of the eye ball; and the compounding effects of the optical sensitivity of the retina and the low numerical aperture of the eye. We have developed two spectral imaging techniques to address these issues. We describe first a system in which a liquid crystal tuneable filter is integrated into the illumination system of a conventional fundus camera to enable time-sequential, random access recording of narrow-band spectral images. Image processing techniques are described to eradicate the artefacts that may be introduced by time-sequential imaging. In addition we describe a unique snapshot spectral imaging technique dubbed IRIS that employs polarising interferometry and Wollaston prism beam splitters to simultaneously replicate and spectrally filter images of the retina into multiple spectral bands onto a single detector array. Results of early clinical trials acquired with these two techniques together with a physical model which enables oximetry map are reported.

Hyperspectral Imaging and the Retina: Worth the Wave?

“…Later, liquid crystal tunable filters (LCTF), whether in the illumination path ( Fig. 1 A4) 26 , 28 , 51 – 53 or in the imaging path ( Fig. 1 A3), 54 and tunable laser sources (TLS; Fig.…”

“…23,77 In patients with radiation-related retinopathy, arteriolar and venular OS were lower in the nondiseased fellow eye compared with the ischemic eye. 59 In healthy rabbits, except Primary open angle glaucoma (oximetry) 30,53 Dry and wet ARMD 23 Retinitis pigmentosa 23 Chronic iridocyclitis 23 Stargardt's disease 69 Radiation related retinopathy 59 Choroidal melanoma 79 ARMD and ARM 33,65,66,78 Sub-RPE deposits and peripheral drusen (autofluorescence) 33,65 Flecken in Stargardt's disease, drusen in fibulin 3 deficiency and membranoproliferative glomerulonephritis type 2 versus drusen in ARMD 69 Drusen in ARMD 65,69 Optic nerve head drusen 76 Drusen in ARMD 88 Physiologic Findings Oximetry 26,36,50,51,57,58,60,76,77,87 Macular pigment (lutein and zeaxanthin) 24,76,87 Cytochrome C in retinal neuron culture 29 Organoid maturation in stem cells (free NADH, retinol and retinoic acid) 80 Fluorophore families (as lipofuscin, melanolipofuscin) in RPE 46,47 Oximetry while elevating IOP [70][71][72][73]...…”

Spectroscopic oximetry in the eye: a review

“…[4,31] Alternatively, wavebands may be recorded using separate channels of a three-colour RGB CCD detector with additional spectral filtering to ehance spectral discrimination. [9,38] The majority of multispectral and hyperspectral imaging studies have employed time-sequential filtering of broadband retinal images, utilising either multiple bandpass filters, a liquid-crystal tuneable filter (LCTF), [21,50,51,53,61,62] or an acousto-optic tuneable filter (AOTF) for spectral discrimination. [54,63,64] LCTFs and AOTFs offer the advantages electronicallycontrolled optical waveband switching in short timescales (~ 50 ms and 25 µs respectively), with a wide-variety of accessible wavelengths.…”

Advances in the understanding of ocular blood flow in glaucoma

“…A linear relationship exists between the oxygen saturation and the ratio of optical densities measured at the two wavelengths. This allows for direct and quantitative mapping of retinal biochemistry [60]. Retinal oxi metry is a novel technology that may help investigators understand the metabolic changes that may contribute to the pathology of glaucoma.…”